| 摘要 | SO2是导致降水呈酸性的主要原因之一。由化石燃烧排放的大量SO2进入大气后，通过植物气孔进入叶肉细胞产生水合作用，形成SO32-、HSO3-和SO42-等形式。SO42-可以被植物吸收、转化、累积和利用，并且是主要的S利用形式，因为大多数植物都有吸收SO2的能力，分析植物组织具有更好的灵敏度和重现性。本研究基于植物组织稳定硫、氧同位素技术，对植物叶片对大气硫沉降的响应进行了详细分析。 本研究选择了马尾松作为研究对象，并选择了大气SO2浓度水平各不相同的多个地区作为采样点，主要包括贵阳地区和云南地区（曲靖、昆明、安宁、晋宁），还选取了两个特定污染点源，曲靖火电厂和昆明钢铁厂，按照离工厂的距离进行采样。采集了各样点的针叶和根际土壤样品，分析测定了针叶的总硫（ST）、硫酸盐硫（SSO4）含量和硫同位素组成、针叶溶解性硫酸盐和叶水的氧同位素组成；土壤硫含量、硫同位素组成和土壤硫酸盐的氧同位素组成。探讨不同生境下针叶对大气硫沉降的差异响应，获得了一些发现和结论： 1.不同地区针叶硫含量比较 各地区大气SO2浓度和针叶硫酸盐硫（SSO4）含量存在较好的正相关关系(y = 0.724x + 0.0107, R2=0.92, P<0.05) ，表明针叶中SSO4含量能够有效可靠地反映大气硫污染水平。但各地SO2浓度和针叶总硫（ST）含量不存在显著相关关系(y = 0.4609x + 0.1441, R2 = 0.27, P=0.36)。表明针叶组织SSO4含量的变化相对于ST含量更能可靠地反映大气硫输入。 植物长期暴露于高SO2环境中，趋向于增加SSO4含量和ST含量，而有机硫含量通常比较稳定，受到影响较小。不同SO2浓度地区的植物根际土壤的总硫浓度差异不大，表明土壤的供硫水平差别不大。从土壤中吸收的硫在不同采样点之间没有明显的不同，叶片SSO4含量的变化可以归因于大气SO2浓度的变化。 2.特定点源针叶硫含量比较 马尾松针叶中SSO4和ST含量总体都表现为随着离工厂距离的变大而降低，这是由于越靠近燃煤工厂，大气SO2浓度越高，SO2和小于1微米的颗粒物能够通过植物的气孔被叶片吸收。长期的煤燃烧污染使得植物叶片中总硫和无机硫浓度都增加，植物叶片吸收过量的硫，超过代谢需求的硫就以SO42–的形式在植物中储存。根际土壤总硫含量比较稳定，不随着离工厂距离变化而变化。叶片硫含量的增加可以归因于燃煤锅炉产生的SO2和颗粒物的污染。 3. 不同采样点针叶组织硫同位素组成比较 贵阳地区针叶中δ34SSO4主要受到燃煤来源的大气硫沉降的影响。贵阳市苔藓组织硫同位素组成、雨水硫同位素组成、针叶硫同位素组成都偏负，相差不大，说明针叶组织硫同位素组成也能指示其长期吸收的硫来源。云南地区针叶中δ34SSO4低于燃煤的δ34S，这是由于同时受到了土壤硫来源的影响。点源附近针叶中δ34SSO4受到燃煤来源的大气硫沉降的控制。 4. 针叶组织总硫和硫酸盐硫同位素组成比较 不同地区和特定点源的各个采样点，δ34ST和δ34SSO4的差值Δ34S(δ34ST-δ34SSO4)大部分分布在2‰-3‰之间，呈现正态分布。证明了植物体内的硫同化过程中只发生很小的同位素分馏。 5.针叶组织硫酸盐氧同位素组成示踪硫酸盐来源 在大气SO2浓度很低的晋宁地区，针叶δ18OSO4接近于土壤δ18OSO4，表明针叶硫酸盐大部分来源于根际土壤。但在其他大气SO2浓度相对较高的地区（曲靖、昆明、贵阳），针叶δ18OSO4远低于土壤和雨水δ18OSO4，表明针叶硫酸盐有相当一部分来源于大气SO2氧化。 SO2氧化生成硫酸盐的氧同位素组成（δ18OSO2）取决于参与反应叶水的氧同位素组成。叶水δ18OH2O与针叶硫酸盐δ18OSO4呈正相关关系(y=0.71x+0.86，R2=0.98, P=0.01)。根据前人的研究结果和计算公式，只要测得针叶叶水δ18OH2O，就能计算出δ18OSO2。根据δ18OSO2与土壤δ18OSO4就能计算出SO2对针叶硫酸盐的贡献率。 贵阳地区大气SO2对针叶硫酸盐的贡献率最高为88%，晋宁地区最低，SO2的贡献率只有33%，这也进一步证实了之前的推断，在大气SO2浓度很低的地区，针叶硫酸盐大部分来源于根际土壤。大气SO2对针叶硫酸盐的贡献率与大气SO2浓度呈对数相关关系（y=20.78ln(x)-8.18, R2=0.87, P<0.05）。 在两个点源昆明钢铁厂和曲靖火电厂附近，针叶的硫酸盐主要有三个来源：直接从土壤吸收、大气SO2氧化，还有在工厂烟道内高温环境下氧化生成的初生硫酸盐。初生硫酸盐造成针叶δ18OSO4随着距离工厂距离的变大而降低。 6. 针叶组织与土壤硫酸盐硫、氧同位素组成比较 在本研究中，不同地区和特定点源针叶组织中硫酸盐的δ34S与土壤中硫酸盐的δ34S都有较好的正相关关系，但针叶硫酸盐的δ18O与土壤中硫酸盐的δ18O没有正相关关系。表明大部分地区针叶中硫酸盐并不是主要来源于土壤。而土壤受降雨、降尘等影响导致其同位素组成变化，也可归因于大气硫沉降引起的差异。 综上，针叶SSO4含量能够很好响应大气SO2污染水平。针叶δ34SSO4能够有效的示踪大气硫来源。针叶δ18OSO4能够指示针叶硫酸盐的来源。 |
| 其他摘要 | SO2 was one of the leading causes of acidic precipitation. After a large amount of SO2 by burning emissions into the atmosphere, entered mesophyll cells through the stomata to produce hydration and formed into SO32-, HSO3- and SO42-, etc. SO42- could be absorbed, transformation, accumulation and utilization by plants. Moreover，SO42- was the main use of form of sulfur. Vegetation was an effective indicator of the impact of a pollution source in its vicinity because most plants had the ability to absorb SO2. Hence analyzing plant tissues could give better results in terms of sensitivity and reproducibility. This thesis based on foliar sulfur and oxygen isotope technique, the response of plant tissues to atmospheric sulfur deposition was systematically studied. The Chinese red pine (Pinus massoniana Lamb) was selected because it met many of the requirements of a good bioindicator plant. This study was carried out in Guiyang and Yunnan areas. Four sites in the Yunnan area including Jinning, Anning, Kunming and Qujing and three sites in the Guiyang City were chosen for needles and soil collection. Two point polluted areas (the Kunming Steel and the Qujing Power Plant) were also chosen for needle and soil sampling. The inorganic sulfur and total sulfur concentrations and their sulfur isotopic signatures, the oxygen isotopic signatures of water soluble sulfate in needles and soil were investigated. We discussed the mechanisms of foliar δ34S and δ18O responses to atmospheric sulfur deposition in different habitats. Some significant innovations have been obtained: 1. Variation characteristics of needles sulfur content in different sampling areas The concentration of water soluble sulfate in the needles was found to be significantly correlated with ambient sulfur dioxide (y = 0.724x + 0.0107, R2=0.9176, P<0.05), but no correlation was seen between total sulfur concentration and ambient sulfur dioxide (y = 0.4609x + 0.1441, R2 = 0.27, P=0.36), indicating that sulfate concentration in needles was more reliably to reflect ambient sulfur input relative than the total sulfur concentration. Chronic SO2 exposure tended to increase the level of sulfate-sulfur and total sulfur in plants whereas the organic sulfur pool frequently remained less affected, since the foliar organic sulfur fraction reflected the process of assimilation of S by plant tissue while the sulfate fraction reflected the process of accumulation of S by the plant tissue. The soil sulfur concentrations from different sites changed little, implying that the level of sulfate supply was little difference in different sites. Hence sulfate in needles should come mostly through absorption from the leaf surface. 2. Variation characteristics of needles sulfur content in two point polluted areas The sulfate-sulfur and total sulfur concentrations in leaves around Kunming Steel Plant and Qujing Power Plant decreased with the distance from the factories. It was due to the closer to the coal-fired plant, the atmospheric SO2 concentration was higher, particulate matter in a size of 1 μm or less can be taken up via the stomates. The long-term coal-burning pollution resulted in enhanced concentrations of the total sulfur and sulfate in the leaves. The uptake of sulfur by leaves had exceeded the metabolic requirement of plants and the excess of sulfur was stored as SO42- .The soil sulfur content did not change with the distance to the factories. It implying that the leaves of Pinus massoniana Lamb were good bioindicator in point polluted areas. 3. Variation characteristics of needles δ34S in different sampling areas The δ34SSO4 in needles was mainly affected by coal-derived atmospheric sulfur deposition. The δ34SSO4 changed little in needles, moss and precipitation at Guiyang, showing that δ34S of needles could also indicate its long-term absorb sulfur source. The δ34SSO4 values in needles negative than that in coal at Yunnan may be related to the influence of 34S-depleted soil sulfur. The δ34SSO4 in leaves was a good indicator of atmospheric sulfur deposition. 4. Variation characteristics of needles δ34SSO4 and δ34ST The δ34ST values were slightly higher than δ34SSO4 values of the needle samples, Δ34S (δ34 ST- δ34 SSO4) for most needle samples was within range of +2 ‰ to +3 ‰, demonstrating that little isotopic fractionation accompanies were happened during sulfur assimilation process in Pinus massoniana Lamb needles. 5. Oxygen isotopic signatures of water soluble sulfate in needles indicating sulfate sources The δ18OSO4 values in needles at Jinning sites where the sulfate concentrations were quite low in needles closed to that of soil, suggesting that the sulfate in needles mainly derived from soil sulfate. In contrast, in the other sampling areas where SO2 concentrations were higher (Qujing, Kunming, Guiyang), δ18OSO4 values in needles were significantly negative than that in soil, indicating that some of the sulfate in needles derived from atmospheric SO2 oxidation. The δ18O value of the SO42- is dependent upon the δ18O value of the associated water. In this study, the δ18OH2O values of leaf-water were significantly correlated with the δ18OSO4 values of needles (y=0.71x+0.86, R2=0.98, P=0.01). According to previous research results, if the δ18OH2O values of leaf-water have been measured, the δ18O of sulfate which derived from SO2 oxidation (δ18OSO2) could be calculated. In different study areas, according to the δ18OSO2 values and δ18OSoil values, the contribution rate of SO2 to water soluble sulfate in needles could be calculated. At Guiyang, the contribution rate was highest and reached up to 88%. On the contrary, the contribution rate was lowest and only 33% at Jinning. It was correlation between the contribution rate of SO2 to water soluble sulfate and the atmospheric SO2 concentration, showing logarithmic relationship. Near the two factories, the δ18OSO4 values in needles trend to decrease with distance from the factories both at Kunming Steel Plant and Qujing Power Plant, suggesting that the change of the δ18OSO4 values in needles is mainly affected by ‘primary’ sulfate around the point pollution source. 6. Variation characteristics of sulfate δ34S and δ18O in needles and soil The δ34SSO4 values in needles in both different areas and two factories significantly positive correlated with the δ34SSO4 values in soil, but no correlation was seen between the δ18OSO4 values in needles and the δ18OSO4 values in soil, showing that the sulfate in needles was not mainly derived from the soil. And that, soil isotopic composition were affected by precipitation, dustfall, etc, could also be ascribed to the variations of atmospheric sulfur deposition. It implied that the positive correlation between the δ34SSO4 values in needles and soil was not the result of sulfate taken up by the root from soil. |
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